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American Institute of Aeronautics and Astronautics

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Evolvable Mars Campaign Long Duration Habitation

Strategies: Architectural Approaches to Enable Human

Exploration Missions

Matthew A. Simon

NASA Langley Research Center, Hampton, VA, 23681, USA

Larry Toups

NASA Johnson Space Center, Houston, TX, 77058 USA

A. Scott Howe

Jet Propulsion Laboratory, Pasadena, CA, 91109 USA

Samuel Wald

Georgia Tech, Atlanta, GA, 30332 USA

The Evolvable Mars Campaign (EMC) is the current NASA Mars mission planning effort

which seeks to establish sustainable, realistic strategies to enable crewed Mars missions in

the mid-2030s timeframe. The primary outcome of the Evolvable Mars Campaign is not to

produce “The Plan” for sending humans to Mars, but instead its intent is to inform the

Human Exploration and Operations Mission Directorate near-term key decisions and

investment priorities to prepare for those types of missions. The FY’15 EMC effort focused

upon analysis of integrated mission architectures to identify technically appealing

transportation strategies, logistics build-up strategies, and vehicle designs for reaching and

exploring Mars moons and Mars surface. As part of the development of this campaign, long

duration habitats are required which are capable of supporting crew with limited resupply

and crew abort during the Mars transit, Mars moons, and Mars surface segments of EMC

missions. In particular, the EMC design team sought to design a single, affordable habitation

system whose manufactured units could be outfitted uniquely for each of these missions and

reused for multiple crewed missions. This habitat system must provide all of the

functionality to safely support 4 crew for long durations while meeting mass and volume

constraints for each of the mission segments set by the chosen transportation architecture

and propulsion technologies.

This paper describes several proposed long-duration habitation strategies to enable the

Evolvable Mars Campaign through improvements in mass, cost, and reusability, and

presents results of analysis to compare the options and identify promising solutions. The

concepts investigated include several monolithic concepts: monolithic clean sheet designs,

and concepts which leverage the co-manifested payload capability of NASA’s Space Launch

System (SLS) to deliver habitable elements within the Universal Payload Adaptor between

the SLS upper stage and the Orion/Service module on the top of the vehicle. Multiple

modular habitat options for Mars surface and in-space missions are also considered with

various functionality and volume splits between modules to find the best balance of reducing

the single largest mass which must be delivered to a destination and reducing the number of

separate elements which must be launched. Analysis results presented for each of these

concepts in this paper include mass/volume/power sizing using parametric sizing tools,

identification of unique operational constraints, and limited comments on the additional

impacts of reusability/dormancy on system design. Finally, recommendations will be made

for promising solutions which will be carried forward for consideration in the Evolvable

Mars Campaign work.

https://ntrs.nasa.gov/search.jsp?R=20160006311 2020-06-12T15:43:18+00:00Z


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Nomenclature

ACS = Attitude Control System

ALSSAT = Advanced Life Support Sizing Analysis Tool

ARV = Asteroid Redirect Vehicle

CC&DH = Command, Control, and Data Handling

CDF = Capability Driven Framework

Delta-V = Change in velocity

ECLS = Environmental Control and Life Support

EMAT = Exploration Maintainability Analysis Tool

EMC = Evolvable Mars Campaign

EOL = End of Life

EPCU = Electrical Power Control Unit

EVA = Extra-Vehicular Activity

EXAMINE= EXploration Architecture Model for IN-space and Earth-to-orbit

GN&C = Guidance, Navigation, and Control

HEOMD = Human Exploration and Operations Mission Directorate

ISS = International Space Station

MER = Mass Estimating Relationships

MLI = Multi-Layer Insulation

MMH = Monomethylhydrazine

NTO = Nitrogen Tetroxide

PEV = Planetary Excursion Vehicle

PMAD = Power Management And Distribution

PV = Photovoltaic

RCS = Reaction Control System

SEP = Solar Electric Propulsion

SLS = Space Launch System

USA = Universal Separation Adapter

I. Introduction

ASA is developing a “long-term strategy for achieving extended missions to Mars” with a goal of reaching the

Mars vicinity with crew in the mid-2030s1. The Evolvable Mars Campaign1,2 (EMC) is an ongoing study

investigating potential options for exploration missions to achieve this goal sustainably and affordably. This study is

distinguished from other Mars mission planning efforts by its focus on reduction of the cost of Mars missions

through the use of evolving near-term investments and reusable vehicles across a cadence of missions building up to

Mars surface missions. It leverages a Capability-Driven Framework (CDF) strategy to phase development costs;

incrementally and strategically developing capabilities in order to enable a continual cadence of progressively more

challenging missions which build upon previous investments. For example, the development of low-thrust

transportation stages and long-duration habitation capabilities enable a mission to deep space and Mars moons. The

addition of capabilities to land and live on planetary surfaces enable additional missions such as a long duration

Mars surface mission. This cadence of missions allows a gradual buildup of capabilities necessary for Mars surface

missions over a longer period of time, reducing up-front spikes in the budget; improving the likelihood of Mars

missions in a fiscally constrained environment. The EMC mission design efforts also reduce the cost of future Mars

missions through the adoption of commonality and reusability on some of the elements including the low-thrust

propulsion stages and short- and long- duration habitats. EMC mission concepts reuse a single transit vehicle and

return to a single Mars surface landing site to reduce the number of production units which must be manufactured

and launched. Additionally, the EMC leverages commonality in the design of habitation systems (both long and

short duration) to eliminate some of the cost associated with new, unique designs. The FY’15 EMC effort focused

upon analysis of integrated mission architectures to identify technically appealing transportation strategies, logistics

build-up strategies, and vehicle designs for reaching and exploring Mars moons and Mars surface.

Long-duration habitation for in-space and planetary surfaces represents a major capability within in the

capability-driven Evolvable Mars Campaign. Habitats must be able to support four crewmembers for 300-1100 days

in challenging environments with limited resupply, no crew abort, and long communication delays; all within

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constrained mass, volume, and power budgets2,3,4,5. In addition to these constraints, there are several characteristics

of the EMC mission architecture which drive specific habitation design strategies. First, the design and manufacture

of each new exploration element tend to be costly, so there is a desire within EMC to develop one common, long-

duration habitat system design (made up of one or multiple modules). These common modules share a common

manufacturing infrastructure and outfitting can be used to build several versions with the appropriate modifications

for transit, Mars moons, and Mars surface missions. Second, the current EMC in-space transportation and Mars

landing performances place mass constraints on the habitat system. This makes large, monolithic habitat concepts

(>40 metric tons) unwieldy for mission planning. For example, identified limitations of in-space delivery

capabilities (specifically electric propulsion performance) have restricted Mars lander options to those capable of

delivering payloads less than 18 metric tons (with options of up to 27 tons possible with additional investment in

entry/landing technologies). This may require habitats to be delivered in multiple modules or as a single module

which can be launched relatively empty and supplied with logistics and spares on the surface. Finally, there is a

desire in the Evolvable Mars Campaign to reuse habitat systems for multiple missions with long periods of

dormancy separating missions. This places additional requirements and design constraints on systems for

refurbishment, repair, and recertification. Based upon these factors, there is a desire within the Evolvable Mars

Campaign analysis work to investigate lightweight monolithic and modular habitat approaches and consider

additional architectural/technological methods to further reduce the mass and improve reusability.

This paper describes various habitation strategies aimed at achieving these EMC goals. Section 2 describes the

three habitats which are needed within the EMC, outlining the constraints and assumptions feeding current habitat

designs. This section also outlines the methodology used to model these habitats to inform transportation and surface

infrastructure analyses. Section 3 describes monolithic (single module) approaches including clean sheet designs and

a concept using the cargo area within a stage adapter on crewed SLS flights as a habitable volume. Section 4

describes modular design concepts aimed at enabling smaller Mars landers. Finally Section 5 describes the

implications of these findings and outline future work to refine habitat concepts.

2. Long-Duration Habitat Design Assumptions and Constraints

1. Habitat types and functional assumptions

There are three long-duration habitat systems in the Evolvable Mars Campaign:

1) a Mars moons habitat available in 2028 supporting crew for 300-550 days

2) a transit habitat available in 2032 supporting crew for up to 1100 days in deep space

3) a Mars surface habitat available in 2035 supporting crew for 300-550 days on the Martian surface

Each of these habitats support a crew of four, providing all required logistics and spares and varying amounts of

power generation, power storage, and EVA functionality for each mission. Additionally, these habitats must keep

crewmembers healthy and happy for all stages of increasingly challenging long duration missions with few

opportunities for resupply or abort. These vehicles require hundreds of cubic meters of volume to accommodate

support systems (including deep space communications, vehicle control, life support, etc.), crew activities (including

meal preparation, exercise, sleeping quarters, etc.), EVA support, psychological acceptable layouts, and logistics

access and storage. The habitats must also be designed to operate reliably for long durations with considerations like

maintainability and supportability in mind. The full list of functional assumptions for long-duration EMC habitats

are listed below:

Habitat Structure & Mechanisms

Metallic cylinder, Al-Al face sheet,- honeycomb structure

25 m3/person habitable volume

Secondary structure sized as 2.46 kg/m2 of habitat structural area

Integration structure 2% of habitat gross mass

4 x 0.5m windows

1 exterior hatch for contingency EVAs

3 docking mechanisms – 1 active, 2 passive

Atmospheric Pressure = 101.3 kPa (14.7 psia), 21% oxygen

Protection

20 layers Multi-Layer Insulation (MLI) covering external habitat surface for passive thermal control

Power

Habitat solar arrays provided when propulsion stage power is not sized to support the habitat


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Electrical Power Control Unit (EPCU) 120 V dc Power Management and Distribution (PMAD) (92%

efficient)

Variable numbers and sizes of Li-ion batteries to support transitions and eclipses

Environmental Control and Life Support (ECLS)

Scaled ISS-level, partially closed ECLSS hardware for 380 days

+10% added life support mass for advanced maintenance and diagnostics

30 days open loop contingency consumables for critical subsystems (carbon dioxide removal, oxygen

generation, water recovery)

Includes fire detection and suppression

Crew Accommodations

Food storage, individual crew quarters, sink(spigot), microwave oven, hand/mouth wash faucet, washer &

dryer, 2 vacuums, laptop, trash compactor, printer, hand tools & accessories, test equipment, ergometer,

photography equipment, exercise equipment, treadmill, table (microgravity)

Extra-Vehicular Activity (EVA)

Assumed 6 m3 volume for internal contingency airlock (consistent with minimal airlock), 90% EVA air

reclamation

Contingency EVAs at a rate of one 2-person EVA per month

Thermal Control

External fluid loop for heat acquisition using ammonia

Internal fluid loop for heat acquisition using 60% prop glycol/water

Heat acquired from cabin & avionics rejected using ISS-type radiators w/ 10 mil Ag-Teflon coating

(parametrically determined from power loading)

Avionics

Provide Command, Control, and Data Handling (CC&DH), Guidance, Navigation, and Control (GN&C) and

Communications

Vehicle Control

Provide 125 m/s delta-V with nitrogen tetroxide/monomethylhydrazine (NTO/MMH) storable propellants

when vehicle must perform maneuvers independent from attached propulsion stages

Utilization

1000 kg unallocated utilization mass + 250 kg robotic assistant

Reserves

Margin growth Allocation - 20% of basic mass

Project Manager’s Reserve - 10% of basic mass

In addition to these functional assumptions, a set of additional transportation system dimensions and mass

constraints guide the design of the single, common habitat design which serves as the basis for the three long-

duration EMC habitats. This habitat design needs to be as mass efficient as possible as the power levels of the

Asteroid Redirect Vehicle (ARV)6 Solar Electric Propulsion (SEP) systems being utilized in the architecture are at

their limits for the transit habitat and delivery of the landers to Mars orbit. The habitats must be able to meet the

mass constraints listed in Table 1 for the current transportation architecture (propulsive element designs and number

of launches) to be feasible. Additionally, the habitats must also be able to be packaged with some other architectural

elements within the currently assumed cargo SLS shroud. Meeting these constraints while providing the required

functionality is a significant challenge. In particular, meeting the 18 ton Mars surface landing constraints currently

being assumed by EMC has been a focus of recent habitation design efforts.

Table 1. Mass constraints for long-duration EMC habitats

Vehicle Mass Constraint

Mars Transit Habitat Gross mass < 40 metric tons

Mars Moons Habitat Total between Mars moons habitat, rover, and landing/mobility equipment

gross mass < 40 metric tons

Mars Surface Habitat Landed mass < 18 or < 27 metric tons (after offloading logistics and other

offloadable items.)


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In order to create a functional habitat design which meets these constraints, several technologies and design

features are assumed. In particular, the following advances are needed to enable EMC architectures:

Lightweight structures

Reliable, component level maintainable life support equipment with ISS level closure

Some combination of low mass countermeasures, pharmaceuticals, crew selection, and revised risk posture to

enable low mass for galactic cosmic ray radiation

Advances to reduce spares mass

Low mass exercise equipment (< 1000 kg) occupying <2m3 volume when stowed

Low mass behavioral health countermeasures

Low mass microgravity physiological countermeasures

High data rate forward link communications

Communications delay-tolerant equipment and operations

Autonomous vehicle systems monitoring and management

Additional advances which are being investigated include repurposing of expended logistics, in-situ manufacturing

of spares, robotic assistants, and inflatable structures applications.

2. Habitat Modeling

In order to investigate various habitat design strategies which can 1) meet these constraints and 2) perform

favorably in the current EMC transportation architectures, a parametric habitat design trade study is conducted

utilizing a parametric sizing tool based upon EXAMINE (EXploration Architecture Model for IN-space and Earth-

to-orbit)7. EXAMINE is an architecture modeling framework developed at NASA LaRC which contains a collection

of parametric performance and sizing tools and algorithms that enable users to model a various types of architectural

elements. Originating from a collection of existing NASA spacecraft sizing toolsets, it includes and expands upon

JSC’s Envision7, MSFC’s MER (Mass Estimating Relationships) database, JSC’s ALSSAT (Advanced Life Support

Sizing Analysis Tool), and a dynamic spares sizing tool EMAT (Exploration Maintainability Analysis Tool)8.

EXAMINE provides detailed architecture element-specific sizing in mass, volume, and power for Levels 1, 2, and

(occasionally) 3 detail. It also provides a framework for performing an integrated sizing analysis across all elements

in an architecture concept, which enables trades studies to improve DRM and element designs.

Inputs are varied in an instantiation of the EXAMINE model created to parametrically size conceptual habitation

elements. This habitat sizing model is then used to investigate multiple habitation strategies to find the right balance

between several factors influencing the EMC transportation architecture. First, a balance must be struck between

vehicle mass and the cost of technologies required to achieve those masses. Architectural and systems-level

integration solutions which require only strategic investment in a few technologies will be preferred over multiple

technology-only solutions achieving similar mass savings. Additionally, habitats should emphasize mission

architecture simplicity which is characterized by reduced numbers of launches, landers, vehicle rendezvous, and

infrastructure setup operations. This simplicity greatly reduces overall mission cost and risk while increasing

feasibility of the architecture by requiring the development of fewer elements. Finally, options which leverage

existing developments greatly reduce development cost, normally at the expense of more mass.While clean-sheet

options optimize mass, they represent a brand new element design. Existing or commercially available elements can

potentially provide cost savings, though an in-depth cost analysis is necessary to validate anticipated benefits.

There are two primary approaches investigated in the EMC for long duration habitats: monolithic and modular.

Monolithic indicates that all of the functions required to support the crew during the mission are located within a

single module. Modular approaches rely on the aggregation of multiple modules to provide all of these functions.

The following sections detail some options for each and comment upon their potential benefits and weaknesses over

alternate approaches. As there are multiple transportation architectures being considered within the EMC, all

concepts shown in this paper are associated with the Hybrid SEP-chemical architecture detailed in Reference 4

II. Monolithic Habitat Design Options

A. Clean-Sheet Monolithic Concepts

Clean-sheet monolithic concepts are the most basic of the habitat design strategies. They feature a custom-sized

habitat sized to include all the required functionality and volume to support crew within one module. Figure 1 shows

an example of an EMC monolithic habitat sized for an 1100 day Mars transit and Table 2 shows the logistics loading


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for the Hybrid Sep-Chemical architecture over the proposed opportunities. The benefit of clean sheet monolithic is

its simplicity and relatively low mass for the total habitation system. Since modular concepts must add hatches,

bulkheads, and other redundant spacecraft systems, they are inherently more massive for a similar overall volume

when compared to monolithic concepts. The major disadvantage of the monolithic habitat strategy is the inability to

lower the delivered mass of the large habitat beyond a certain threshold.

Design Constraints/Parameters Category Mass, kg

Structure 5,185

Max Crew Capacity 4 Protection 268

Max Crewed Mission Duration 1100 d Propulsion 0

Destination Earth-Mars Transit Power 1,980

Pressurized Vol. 210.7 m3 Control (ACS/RCS) 0

Habitable Vol. 100.0 m3 Avionics 453

Logistics Storage Vol. 64.7 m3 ECLSS 3,507

Operating Pressure 101.4 kPa EVA systems 2,425

Oxygen Fraction 21.0 % Thermal Control System 1,115

ECLSS Closure - Water Partially Closed Crew Equipment 1,749

ECLSS Closure - Air Partially Closed Utilization 1,000

Habitat Structure 3 - Vertical Rigid Cylinder

Growth 5,172

Habitat Length 5.92 m DRY MASS SUBTOTAL 22,854

Habitat Diameter 7.20 m Logistics including ECLSS Consumables (Nominal + Contingency)

See Table 2 Team Data Radiation Protection Layout / logistics

placement Reserve and Residual Prop. 0

EVA Capability Internal suitlock INERT MASS SUBTOTAL xxx

Number of EVAs out of hab 74 person-EVAs Propellant 0

RCS Engine Type None TOTAL WET MASS xxx

RCS Propellant None Power Generation None

Power Storage Li-ion batteries

EOL Power Required 21.3 kW

05-19-2015 Image not to scale

Total battery energy storage 263 kW-h Description Power load during battery

operation 16.1 kW

Mars transit habitat vehicle sized for mission duration plus contingency duration for Hybrid architecture. It includes an internal suitlock for contingency EVAs, which are assumed at one 2-person EVAs each month. Power generation provided by PV arrays on the habitat.

Mass Growth Allocation 20%

Project Manager's Reserve 10%

Dormant Power (uncrewed) 3.5 kW

Transit Power (crewed) 13.6 kW

Figure 1. Mars transit habitat baseball card - 1100 days

Table 2. Logistics loading of habitat for various opportunities

NOTIONAL


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For example, the mass breakdown shown at the right hand side of Figure 1 shows a habitat dry mass of ~23 tons.

The dry mass of Mars surface and Mars moons habitats is similarly ~21-23 tons, with variations due to outfitting.

These masses do include a few items that would be offloadable, but ideally this would represent the indivisible

delivered mass of the transit habitat if all logistics were delivered separately. As ~22 tons is more than the desired 18

tons for small Mars surface landers, this dry mass is problematic. An offloading analysis performed to address this

issue shows that removing additional offloadable components can reduce the Mars surface habitat mass down to a

minimum of ~17 tons which would enable the habitat to be delivered on an ~18 ton lander with approximately 30

days of logistics for crew. However, the amount of offloaded components greatly increases the complexity of the

setup operations and somewhat increases the risk to crew by requiring critical rendezvous on the surface with

logistics modules. Additionally, this places the loaded mass of the habitats right against the ~18 ton threshold, which

makes it susceptible to becoming infeasible when/if habitat mass grows. This additional complexity and lack of

margin are the main challenges of implementing a monolithic surface habitat on a ~18 ton surface lander.

There are a few ongoing design efforts refining habitat designs to determine if monolithic surface habitat

approaches can meet the 18 ton constraint without over-complicating the surface/landing operations. Additional

investigations in EMC are currently underway to determine if developing a more capable lander somewhere between

18 and 27 tons can enable a more desirable architecture with fewer total launches/landers.

B. SLS Universal Stage Adapter – Derived Monolithic Concepts

Another approach being investigated in the EMC is geared at allowing habitat elements to be launched upon

crewed SLS launches to fully utilize the available launches to aggregate exploration elements. Several

configurations have been proposed for a SLS Universal Separation Adapter (USA) that will be used between the

Exploration Upper Stage (EUS) and the Orion Crew Exploration Vehicle (CEV). Studies were conducted to

determine whether habitation elements could be carried within the USA volume, as possible secondary payloads in

an Orion launch. It is assumed that the USA structure would be used as-is, with added pressurized bulkheads to

create a pressurized cabin volume for habitation elements. Additionally, hatches would need to be added to allow for

transfer in and out of the pressurized volume. In effect, the USA volume could allow a habitat to be brought up in

the “trunk” of the launch vehicle, where the Orion SEV is the primary payload. Figure 2 shows an example of

adding a habitation element into a notional USA concept.

SLS stack Unpressurized volume for tankage and equipment Habitation element Orion SEV USA shown partially transparent for clarity

Figure 2. Habitation elements carried in a notional SLS Universal Separation Adapter (USA)

Several options were studied with the USA-derived “trunk” habitats that would allow the Orion SEV to separate

from the stack, dock with the habitat, provide for inflatable habitat volume extension, protect EVA porches, and

provide additional vehicle docking ports (Figure 3). The results indicated that some versions of the “trunk” habitat

concepts are feasible from an operational perspective.

NOTIONAL


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Extended Cone habitat Inflatable EVA porch Orion CEV SLS stack Orion in flight configuration Orion SM shroud remains Inflatable EVA porch stowed Eject portion of USA shroud Inflatable EVA porch deployed EVA hatch at end Logistics module or other vehicles docking at radial hatches

Figure 3. Configuration options for a notional SLS / USA-derived “trunk” habitat

It was assumed that the potential payload capacity for SLS 1B USAs would be ~10 tons and SLS 2 USAs would

be ~15 tons. A study was performed to understand the available volumes which could be created in various USA

geometries and what mass would be available for outfitting of the interior after accounting for the additional

structure required to make an USA pressurizable. Masses for the habitation elements were constrained by the

capacity of the launch vehicle beyond the USA and Orion payload masses. Volumes varied, and were constrained by

the configuration of the various USA options. The results of initial studies are shown in Table 3. Several of the

options enable pressurized volumes on par with those carried in the clean-sheet monolithic similar to the concept

shown in Figure 1. Additionally, combined USA and habitat structure masses of 3-6 tons, leaves 4 to 7 tons (in the

10 ton payload limit) and 9 to 12 tons (in the 15 ton payload limit) for built in outfitting. Based upon the estimated

masses of difficult to offload subsystems like life support, thermal, and power, it seems preliminarily feasible that an

USA-derived habitat concept could be developed.

NOTIONAL


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Table 3. SLS / USA-derived “trunk” habitation element masses and volumes

Option

Habitat Volume

(m3)

Inflatable Volume

(m3)

Total Pressurized

Vol. (m3)

USA Mass (kg)

Habitat Mass (kg)

Inflatable Mass (kg)

Total Mass (kg)

Short Stack 95 95 2,500 686 3,186 Short Stack Inflatable

95 248 343 2,500 686 652 3,838

Cone Cylinder 327 327 5,200 762 5,962 Cylinder Cone 175 175 3,800 1,645 5,445 Extended Cone 260 260 5,200 711 5,900

However, despite being feasible, the potential limitations of USA-derived habitat concepts are numerous. It does

open up the possibility of commercial flights for some of the outfitting flights, but additional analysis is needed to

prove that utilizing this strategy will actually reduce cost, as there is no guarantee it will reduce the total number of

launches. This concept is also sensitive to launch vehicle mass growth. The 10 to 15 ton payload capacity of the SLS

may disappear as additional engineering and manufacturing issues arise in the development of the SLS.

Additionally, this USA-derived habitat concept is the only driver for a larger USA. Launch vehicle designers desire

to minimize the mass of this section of the launch vehicle and currently plan to stage the structure during the ascent.

As it is not clear that this habitat concept is a significant enabler of more effective mission architectures, it is

unlikely that the USA geometry will be protected for its possible development. Ongoing efforts are not currently

planned for these concepts, but may be reintroduced at a later time.

In summary, monolithic options are feasible, but face significant challenges for Mars surface. One option to

correct this is to enforce commonality between transit and Mars moons habitat, but exclude commonality from a

Mars surface perspective by designing a customized Mars surface habitat capable of meeting lander constraints.

Another option is to simply increase lander capabilities to enable a common design between all three Mars mission

habitats. Finally, the final option is to enforce commonality through the three habitats with the existing lander

constraints by splitting them up to reduce the largest single piece which must be landed on the Martian surface. This

does enforce some additional constraints on surface mobility and lander packaging manifests, but shows promise for

achieving leaner missions with reduced landings. The next section describes some ongoing efforts to investigate the

potential benefit of modular habitats in the context of the EMC missions.

III. Modular Habitat Design Options

A. Clean-Sheet Monolithic Concepts

Modular habitat systems have the potential to provide a wide range of benefits to a mission or campaign

architecture. The modular habitat architecture is motivated by mutual interdependencies with other elements and

systems. Moving from a single monolithic structure to multiple smaller habitat modules can help to simplify the

operations required move the elements both on the Martian surface and in microgravity. It also reduces the launch

and lander payload requirements by reducing the mass and size of the largest elements, and allowing for alternative

lander packaging manifests. In addition, modular schemes may also reduce the complexity of resupply operations by

allowing new logistics to be added without requiring the crew to transport tons of cargo between modules for

assembly and storage. Like monolithic approaches, opportunities for commonality of pressure shells and other

systems are also enabled by some modular architectures, which can in turn help to reduce manufacturing costs.

Additional pressure volumes may also serve to reduce risk to the crew due to fire and decompression, allowing them

a safe haven from which to stage and plan a solution to the issue.

However, modular habitation strategies may also bring various downsides and penalties9. Mass penalties are

generally associated with duplicate systems necessary for each module, such as hatches, fire suppression, lighting,

and air distribution and contaminant control. Structural mass penalties are also incurred due to the lower volume to

mass efficiency of smaller radius modules, assuming constant length. Packaging efficiency for launch and landing

may also be decreased if the space between individual cylindrical habitat modules cannot be filled by other

payloads. Finally, modular concepts drive the design of surface offloading and mobility systems. The requirement

for the currently assumed surface offloading and mobility considerations if delivery of modular components less

than 10s ton apiece. Delivery of larger modular pieces will require update of the surface system architecture. Despite


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these downsides, the EMC team is interested in evaluating how modular habitation options could impact the entire

system across the campaign, and has begun to look at a few of the potential modular habitat options.

The EMC habitation team has set out a few modular options for analysis in order to trade them with previously

described monolithic options. These modular options provide the same habitat functionality as the monolithic

habitats split across multiple modules. Two of these concepts are listed below, and are also shown in Figure 4.

Concept A –

o Surface: One large primary habitable and functional volume, with separate logistics modules

under 10 tons to allow for use of mobility systems to move and mate modules

o Moons: Common primary module, larger 500 day logistics module.

o Transit: Common primary module, two 500 day logistics modules.

Concept B –

o Surface: One large primary habitable and functional volume with mass of 18 tons, with

separate logistics and offloadable item modules under 10 tons to allow for use of common 18

ton lander across EMC.

o Moons: Common primary module, larger 500 day logistics module.

o Transit: Common primary module, two 500 day logistics modules.

Note that the “larger 500 day” logistics modules may be split up to enforce small habitat commonality with surface

logistics. Preliminary analysis has shown that these modular options can fit within the current EMC architecture and

may provide more flexibility to the design of other campaign elements.

Figure 4. Clean-sheet modular habitation concepts

Concept B, comprising of one large primary habitation module and multiple smaller logistics modules, allows

for the use of the smallest lander concept of 18 tons, and enables easy movement and rendezvous of the logistics

modules with the larger module. Sizing of this habitat system was completed using the same methods and

assumptions as those of the monolithic concepts. A summary of the surface habitat module masses and volumes, as

well as a comparison can be seen in Table 4. This concept requires three common logistics modules in order to

contain all of the necessary pressurized logistics as well as the offloaded items that must be reassembled by the crew

in the main module upon their arrival. The empty mass penalty for this modular habitat is about 50%, which is

significant if evaluating concepts on habitat mass alone. However, more work is necessary in order to evaluate the

overall campaign-wide impact of these concepts. Lander, propulsion, destination operations, and aggregation teams

will all incorporate this concept and others into their trade space in order to fully understand their implications.


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Table 4. Concept B modular habitation system masses and comparison with monolithic habitat system

Module Empty Mass

(kg)

Outfitted Mass

(kg)

Habitable

Volume

(m3)

Pressurized

Volume

(m3)

Primary 18,003 18,003 100.00 150.66

Logistics 4,035 9,438 8.33 33.30

Logistics 4,035 9,438 8.33 33.30

Logistics 4,035 9,438 8.33 33.30

Total 33,557 46,318 124.98 250.57

Monolithic 22,492 34,531 100.00 183.59

% Delta + 49% + 34% + 25% + 36%

B. Evolvable Modular Habitat Concepts.

All of the habitat concepts investigated thus far in this paper propose new investments to create a workable

habitation system. An alternative approach is to identify several habitable elements that will be available by the first

long-duration habitat launch planned in 2028 that could be assembled into a working, long-duration habitation

system with reduced investment. Additionally, it is anticipated that an initial cislunar habitation system will be

needed in the early 2020s to provide short duration (30-60 days) habitation to prove out long-duration systems and

operations. If a habitat system could be developed which addressed this need as part of its development, the

resulting evolvable strategy could greatly reduce required investments by NASA for some microgravity

applications.

Figure 5. Evolvable modular habitat concept

An evolvable modular habitat concept is currently being investigated at a pre-conceptual level for feasibility. In

this concept, commercially producible elements can be aggregated during SLS crewed launches utilizing the co-

manifested payload capability (10 tons before 2028, 15 tons after 2028). An initial cis-lunar habitat can be

constructed from a Planetary Excursion Vehicle cabin – common airlock and a commercially available logistics

module and service module as shown in Figure 5. This vehicle can be outfitted for 30 day missions under 10 tons.

By adding a commercially producible inflatable habitat near 180 m3 which is less than 15 tons when partially


12

outfitted, the total net habitable volume necessary to support a long duration mission is provided similar to that of

the monolithic concept shown in Figure 1. This resulting habitat system can be ‘topped off’ in two logistics flights

and perform the Mars moons mission, while being aggregated through co-manifested or commercial deliveries.

Similar concepts could also be created for a Mars transit habitat, but Mars surface is anticipated to be too mass

constrained for this approach to be feasible.

Initial concepts have shown that an evolvable habitat concept is feasible under the aforementioned constraint, but

there are several drawbacks to such an approach. First, the 30% increase in mass at trans-Mars injection burn, has

performance impacts on the transportation system, particularly for the transit habitat case which is already near its

40 ton limit. Second, the necessity of 4 launches for a single mission is considerably more complicated than the

simpler monolithic options. There may be additional issues with long aggregation times on perishable consumables.

Ongoing studies will continue to search for an optimal evolvable modular habitation system which performs well in

the context of the EMC, while the transportation team assesses how the transportation architecture might be adjusted

to enable this potentially lower cost approach.

IV. Conclusion

One important consideration which has not been previously mentioned is the importance of how reusability and

long periods of dormant operations will affect habitat design and the selection of the most advantageous habitation

strategy. The EMC is built upon the premise of reusability, but ongoing work is currently seeking to quantify the

impacts to subsystem designs and masses. It is anticipated that autonomous vehicle health maintenance systems and

substantially modified logistics supplies will be necessary, but the issue of how spares and routine maintenance of

subsystems will be handled is a frequent topic of current team discussion. In addition, long periods of dormancy are

anticipated to be an issue for perishable goods and systems with limited expected lifetimes. Information and

procedures for interrupted occupancy of the International Space Station are being investigated to develop a plan for

these challenges and will be released in the near future.

In summary, several habitation approaches have been described in the previous section. The current baseline

habitat concept being carried in the EMC analysis is the clean-sheet monolithic approach, but the trades described

above are leading the EMC analysis teams to investigate alternate mission architectures while concurrently

developing higher fidelity parametric tools to adequately capture the difference between proposed concepts

independent of large modeling uncertainties. In particular, the EMC team’s near term focus is to understand how the

modular concepts change the transportation architecture.

References 1Craig, D. A., Herrmann, N. B., and Troutman, P. A. “The Evolvable Mars Campaign - Study Status,” IEEE

Aerospace Conference 2015, Big Sky, MT, 2015. 2Craig, D., Herrmann, N., and Troutman, P., “Pioneering Space Through the Evolvable Mars Campaign,” 2015

AIAA Space Conference, Pasadena, CA, 2015. 3Percy, T., McGuire, M., and Polsgrove, T., “In-space Transportation for NASA’s Evolvable Mars Campaign,”

2015 AIAA Space Conference, Pasadena, CA, 2015. 4Merrill, R., Chai, P., Jones, C., Komar, D., and Qu, M., “An Integrated Hybrid Transportation Architecture for

Human Mars Expeditions,” 2015 AIAA Space Conference, Pasadena, CA, 2015. 5Goodliff, K., Cirillo, W., Mattfeld, B., Stromgren, C., and Shyface, H., “Comparison of Human Exploration

Architecture and Campaign Approaches,” 2015 AIAA Space Conference, Pasadena, CA, 2015. 6Mazanek, D.D., et al, “Asteroid Redirect Robotic Mission: Robotic Boulder Capture Option Overview,” 2014

AIAA Space Conference, San Diego, CA, 2014. 6Komar, D. R., Hoffman, J., and Olds, A., “Framework for the Parametric System Modeling of Space

Exploration. Architectures,” AIAA-2008-7845, 2008. 8Stromgren, C., Terry, M., Cirillo, W., Goodliff, K. and Maxwell, A., “Design and Application of the

Exploration Maintainability Analysis Tool,” AIAA Space 2012 Conference and Exposition, AIAA-2012-5323,

Pasadena, CA, 2012. 9Simon, M.A., Toups, L., Smitherman, D., “Potential Applications of Modularity to Enable a Deep Space

Habitation Capability for Future Human Exploration Beyond Low-Earth Orbit,” GLEX-2012.05.3.6 x12574, 2012

Global Space Exploration Conference, Washington, D.C., 2012.

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Evolvable Mars Campaign Long Duration Habitation ... · For example, the development ... EVA support, psychological acceptable layouts, and logistics access and storage. The habitats